As hypervior does not have the knowledge of guest network configuration, it'sbetter to ask guest to send gratuitous packet when needed.

Guest test VIRTIO_NET_S_ANNOUNCE bit during config change interrupt and when itis set, a workqueue is scheduled to send gratuitous packet throughNETDEV_NOTIFY_PEERS. This feature is negotiated through bitVIRTIO_NET_F_GUEST_ANNOUNCE.